I was going to say that if you turned off the pressure, all you had to do was drain the water below the level of the tubing. Does your description mean that the "crimp off" is still on the copper behind the cap?

The problem is that I have hydronic heat in the ceilings of my home - there are 1000's of feet of 1/2" od soft copper embedded in the plaster ceilings. It's a real pain to get the air out, so I didn't want to drain the circuit.

So, in the lower level ceiling, I used a C-clamp and vise grip to close off the 'loop' in the bathroom floor. I cut the copper about 6" before the crimp. The crimp was effective - just a dribble or two of water. That's when I decided to flare the tubing and capped one end of a flare-to-pipe union for a stopper.